Donald lee miles



Patented Feb. 8, 1949 METHOD OF AND MATERIAL FOR PREPAB ING ZINCIFEROUS SURFACES FOR ELEC- TROPLATING Donald Lee Miles, Detroit, Mich., assignor to Paint Company. Ambler. Pa... a corporation oi Delaware American Chemical No Drawing. A

'7 Claims.

This invention relates to a method of. as well as to new materials for. treating surfaces of zinc and zinc base alloys in preparation for an electroplating operation.

The principal objects clean the surfaces prior of the invention are to to the plating operation; to condition the surface so that it will better accept the plate; to improve the quality of the plated article; to minimize blistering or the platin: even when subjected to extremes of temperature; to reduce the number of rejects as well as to make possible the re-processing of rejects which have been cleaned and plated according to conventional methods where my invention has not been employed; and. in general, to improve the art of electroplating zinciferous surfaces.

The invention has been found to be useful as a preparatory step in any of the conventional plating operations familiar to the art, a typical plating sequence being as follows:

1. Treatment according to the present invention.

. Water rinse. Reverse current electroclean. Water rinse. Dilute acid dip.

Water rinse. Copper strike. Copper plate. Water rinse. i0. Nickel plate. 11. Water rinse. 12. Chromium plate.

as follows: Mineral spirits gals 0.3360 Phosphoric acid, 75% gals 0.4853

plication August 11, 1947,

Cyclic coal tar bases gals 0.0144 Sulfuric acid (66 B.) gals- 0.0049 Thiourea lbs 0.0250 Poiymerized ethylene oxide condensate l (100% basis) lbs 0.0135 Water, to make gal 1.0000

l The bases which I have found to be most suitable may be either isolated buses or narrow cuts or the entire extraeled bases from various fractions oi coal tar. For exun in. I ll] use the chemical individuals pyridine, any of the indiv dual iutldines, picnlines or collidines, quillllinv, substituted quinillnvs. etc. (Jr 1 may employ volunwrcial cuts known as crude pyridine bases, crude qninllimfraction, a crude quiniiine fraction from which the nuinliine itself has been removed. vic. A patently bnseu extracted by the usual cnnnm'rcinl met min from any fraction of coal tar are satisfactory. even when certain individuals have been rmnoved from the frnrrion. The bases themselves mny boil over it long range as. for example. from 110' C. to 365' C. or even higher. Some of these buses are known to be oi the pyridine and qniniilne series and others contain hydrogenated rings. in 011% case all the coal iar bases 0 commerce seem to be an a 'll i i s material is a non-ionic wetting agent. the basic characteristic of which is an ethylene oxide chain. on one end of which chain is linked a hydrocarbon radical through an oxygen atom and on the other end is a h;- drol zren atom. he general formula for these compoun s is 0(CH.0)=H where R is a hydrocarbon radical and a generally is between 3 end 30.

As stated, the foregoing formula produces a relatively concentrated material which is preferably diluted with about four parts of water although the degree of dilution may be varied somewhat to meet differing conditions, actual optimum dilution ratios being obtainable by simple experimentation.

I wish to note at this point that some of the ingredients are not soluble in water and that the aqueous treating bath is usually in the form of a relatively stable emulsion. However. I have noticed, at times. that the emulsion partially breaks or separates but that this breaking or separation, apparently, has no deleterious efiect on the operation of the process especially if the bath is somewhat agitated as is generally the case during normal operations of the process.

The diluted material may be applied to a series or succession of the articles being treated in any desired manner although experience to date would indicate that immersion in the bath is probably preferable. the period of immersion being from approximately 30 seconds to appro rimately 2 minutes depending upon the degree and nature enemas of the soil existing on the surface and the temperature of a bath, which latter can range anywhere i'rom about 70 F. to a practical maximum,

I have found that my process of treating zinc and zinc base alloys in preparation for an electroplating operation serves not only to clean the surface but also to condition it in such a way as to greatly improve the character and finish of the final plate. Even grossly contaminated surfaces can be cleaned with my material. the deposits of soil apparently being blown free from the surface by the evolution of hydrogen gas and then rising to the surface of the bath where they are either dispersed or dissolved. Due. possibly to this rapid removal of deposits of soil even in recessed areas such as are usually present on more or less intricately shaped die castings, the subsequent etching of the zinclferous surface is extremely uniform and blistering of the final plate is almost entirely if not completeiy eliminated.

It will be seen. therefore, that in addition to the cleaning operation effected by my process and my material there is also a conditioning of the surface in some way, the nature of which is not altogether clear but which I have found to be of very definite and helpful effect.

I should like to note the fact that the solutions which I use are strongly acidic and that in prior cleaning practice it has been customary to avoid such acid solutions for cleaning purposes due to their tendency to cause the work to become covered with smut. This trouble has been particularly evident with zinc alloys containing relatively high percentages of copper. Indeed, even with my improved material, I have found it inadvisable to apply the process to copper bearing alloys having higher than approximately 1%, copper content if optimum results are to be attained in the subsequent electroplating steps. However, I also wish to emphasize the fact that with my invention it is posible to clean and condition in a satisfactory manner zinc base alloys which have a greater than average content of copper.

One outstanding and very valuable application of my new invention resides in its ability to clean and reeondition articles which have been rejected due to improper plating by conventional cleaning and plating procedures. In other words, where the plating has failed, it is only necessary to strip the plated article down to the zinc surface by any conventional method and then subject the article to treatment according to my invention thereby making it possible to secure a replate which I have found is perfectly satisfactory and meets the most exacting standards for plated work of this kind. This makes possible a great reduction in losses from this source which losses in many industries have been very high. Where the invention is used in the manner Just described the sequence of operations, of course, is preceded by a stripping of the plate from the rejected article followed preferably by a vapor degreasing operation before the article is treated with my improved bath.

I should like to point out that while the formula given above has been found to give exceedingly satisfactory service for which reason I prefer to employ it in the proportions specified, yet it is 5 possible to vary the proportions somewhat especially with respect to the amount of phosphoric acid although a relatively high degree of acidity of the bath is very important. Insofar as the phosphoric acid content is concerned, I have found that fairly good results can be obtained where the phosphoric acid content ranges downwardly from that given in the formula to approximately half of the amount specified or approximately 0.2418 gallon. As for the coal tar bases. I have found that too great a quantity will lead to uneven pitting of the work, smutting and generally to defective surface conditioning. Too little of the active ingredients leads to a lack of cleaning, uneven conditioning and generally defective work.

In conclusion, I have found that my improved treating bath will function satisfactorily for relatively long periods of time although naturally it will become necessary ultimately to completely replace the bath. Until this point is actually reached. however. I found that the efficiency of the bath during the course of treating a series or succession of articles may be maintained simply by the periodic addition of water, wetting agent and mineral spirits in about the following proportions:

Gallons Mineral spirits 0.7000 Polymerized ethylene oxide 5 condensate (100% basis) 0.0282

Water 0.2718

In other words replenishment or refreshment can be effected for a considerable period of time in the manner just indicated and the quality of the finished work will be the best guide to the frequency with which such replenishment or refreshment should be made. This possibility constitutes a somewhat unusual procedure because it would normally be expected that the acid at least would require replacement as soon as any of the other ingredients.

I claim:

1. In the art of electroplating surfaces of zinc and zinc base alloys the step of treating the surface prior to the electroplating operation by sublecting it to the action of an aqueous bath containing the following ingredients in approximately the proportions indicated:

Mineral spirits gals 0.3360 Phosphoric acid -gals 0.24l8to0.4835 Cyclic coal tar bases gals 0.0144 Sulphuric acid (66 Be.) gals- 0.0049 Thiourea lbs 0.0250

60 Polymerized ethylene oxide condensate basis) lbs 0.0135

2. The treatment of claim 1 wherein the temperature of the bath is maintained between about m and w.

3. In the art of preparing a succession of articles having zinciferous surfaces for an electroplating operation the steps which consist of treating fihe surfaces by subjecting them successively to t e action of an aqueous bath containing the following ingredients in approximately the proportions indicated:

Mineral spirits gals 0.3360

75 Phosphoric acid (75%) gals 0.2418 to 0.4835

amas Cyclic coal tar bases ---gais 0.0144 Sulphuric acid (66 B6.) gals 0.0049 Thioutee. ibs 0.0250

Pclymerized ethylene oxide condensate (100% basis) lbs 0.0135 Water, to make approximately-- gals 5.000 and in periodically refreshing the bath by addition thereto 01 a material consisting essentially of the following ingredients in approximately the proportions indicated;

gallons Mineral spirits 0.7000 Polymerized ethylene oxide condensate (100% basis) 0.0282 Water 0.2718

4. The method of claim 3 wherein the temperature oi the treating bath is maintained between about 140 F. and 150 F.

5. An aqueous bath for treating zinciferous surfaces consisting essentially oi' the following ingredients in approximately the proportions indicated: Mineral spirits gals 0.3360 Phosphoric acid (75%) gals 0.2418 to 0.4885 Cyclic coal tar bases gals 0.0144 Sulphuric acid (66 Be.) ga1s 0,0049 Thiourea lb 0.0250 Poiymerized ethylene oxide condensate (100% basis) -ibs 0.0135

6. A concentrated material for treating zinciierous surfacesconsisting essentially of the following ingredients in approximately the proportions indicated:

'1. A material for use in replenishing the bath of claim 1 consisting essentially oi the following ingredients in approximately the proportions indicated:

gallons Mineral spirits 0.7000 Pclymerized ethylene oxide condensate basis) 0.0282

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 379,731 Schoemns Mar. 20, 1888 1,534,446 Gravell Apr, 21, 1925 1,566,241 Whitney Dec. 15, 1925 1,740,731 Gravell Dec. 24, 1929 2,033,444 Nisizawa Mar. 10, 1936 2,311,047 Hagelin Feb. 16, 1943 i Certificate of Correction Peitent No. 2,461,228. February 8, 1949. DONALD LEE MILES It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correctlon as follows:

Column 1, line 47, for 0.4853 read 0.4835; column 4, line 25, before the word found insert have;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 14th day of June, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

